Peptide amphiphiles (PA) are small, synthetic molecules composed of a hydrophobic alkyl tail, a beta-sheet forming peptide sequence, a charged amino acid sequence and a short peptide segment usually containing a bioactive epitope (SEE FIG. 1A) (Hartgerink et al. PNAS 2002, 99, 5133-5138; Hartgerink et al. Science 2001, 294, 1684-1688; herein incorporated by reference in their entireties). Peptide amphiphiles assemble into high-aspect ratio nanofibers (SEE FIG. 1B) upon electrostatic screening of the charged amino acids. In vivo and in vitro studies have shown that certain PA molecules, such as those with IKVAV, RGD or VEGF epitopes, exhibit significant biological activity (Silva et al. Science 2004, 303, 1352-1355; Rajangam et al. Nano Lett. 2006, 6, 2086-2090; herein incorporated by reference in their entireties). PAs and oppositely charged polymers can self-assemble at the aqueous interface of two solutions into hierarchically organized, semipermeable membranes, producing sac-like structures on the macro scale (≧1 mm) (Capito et al. Science 2008, 319, 1812-1816; herein incorporated by reference in its entirety).